Hydrofluoroethane plasma etching of SiN, SiO2, and poly-Si films with CHF2CF3, CF3CH3, and CHF2CH3

Abstract

Plasmas containing hydrofluorocarbon gases (CHF₂CF₃, CF₃CH₃, and CHF₂CH₃) are used for the selective removal of SiN, SiO₂, and poly-Si films when manufacturing large-scale integrated circuits. Understanding the plasma chemistry of hydrofluorocarbons is important for gaining insight into the mechanisms of these selective-etching processes. The fragmental reactants produced by the reactive plasma are essential for evaluating and controlling highly accurate selective etching. This study examined such fragments using a primary dissociation ionization threshold quadrupole mass spectrometer at an electron energy of 20 eV. Their primary dissociative ionization thresholds were identified using photoelectron-photoion coincidence spectroscopy, with photon energies ranging from 10 to 28 eV. The results showed the following: (i) the CHF₂CF₃ molecule dissociated into ions such as CHF₂⁺ and C₂HF₄⁺, which formed secondary ions, such as CF₃⁺ and CF₂⁺. The F-rich reactants effectively enhanced the etching of both SiO₂ and SiN; (ii) the CF₃CH₃ molecule dissociated into ions such as C₂H₂F⁺ and C₂H₂F₂⁺, while the dominant CF₃⁺ remained as a crucial fragment for the primary etching of SiO₂; (iii) the CHF₂CH₃ molecule predominantly yielded ions such as CHF₂⁺, CF₂CH₃⁺ and C_xH_y⁺, promoting polymer film deposition on the surfaces of SiO₂ and poly-Si.